A fault with the signalling system between London Kings Cross / Moorgate and Stevenage means trains have to run at reduced speed on the line towards Stevenage. As a result, trains may be delayed by up to 30 minutes.

Disruption is expected until 16:30.

Customer Advice:

Great Northern and Thameslink

You can travel as normal, but should allow an extra 30 minutes for your journey.

Check station screens and planners for the latest information for your train.

Planning your journey:

You can check train departures from your station here:

• Thameslink live departure boards
• Great Northern live departure boards

You can view live maps of our network here:

• Thameslink live route map
• Great Northern live route map

Can you tell me more about the incident?

We were first advised of a track circuit failure in the Welwyn Garden City area at 15:32 today.

This part of the network uses track circuits to detect the position of trains. These are electrical systems which monitor whether a train is on a section of track. They operate as part of the signalling system, which is designed to be "fail safe".

When a track circuit fails, the signalling system will interpret this as a train remaining in place, even though there may not be a train present at all, or the previous service may have long since left the area.

As a result, further trains cannot be automatically allowed onto the relevant section of track. Train drivers will be stopped by red signals on approach. They will then get verbal permission from the signaller so that they can proceed, and will run at a heavily-reduced speed as far as the next signal. This is so that the drivers will stop safely if they see anything ahead of them.

In some areas, the sections between signals can be several miles long, so this can result in delays building up. Even with shorter sections of track affected, there would still be a delay of at least a few minutes to each journey.

Track circuit faults can be caused by a number of different issues, including electronic faults or obstructions on the track. Network Rail manage the signalling system, including track circuits, and their staff will be investigating as quickly as possible.

Check before you travel:

You can check your journey using the National Rail Enquiries real-time Journey Planner.

Compensation:

You may be entitled to compensation if you experience a delay in completing your journey today. Please keep your train ticket and make a note of your journey, as both will be required to support any claim.